1. Field of the Invention
The present invention relates generally to a computer system including a data storage system. More particularly, the invention relates to a system and method for the incremental packet recording of recordable compact discs.
2. Description of the Background Art
A Compact Disc-Read Only Memory (CD-ROM) disc offers massive storage capacity, currently over 600 megabytes (Mb) of data, and can store digital information for retrieval using a random access technique. As its name implies, a CD-ROM disc is not usable as a writable medium, i.e., the data on a CD-ROM disc cannot be changed once the disc is formed during the manufacturing process.
Unlike a CD-ROM disc, a Compact Disc-Recordable (CD-R) disc is usable as a writable medium. A limitation of CD-R, however, is that the medium can be written to only once. Hence, CD-R is also known as Compact Disc-Write Once (CD-WO). Once a portion of a CD-R disc is written, that portion cannot be erased or rewritten.
As a result of this limitation and other considerations, it has been common in the past for systems to write to an entire CD-R disc in one uninterrupted stream. Nevertheless, incrementally updating of a CD-R disc can be done using incremental recording techniques.
Currently, incremental recording techniques include recording a track at once (TAO), and packet recording (PR). PR can be accomplished by Fixed Packet Recording (FPR) or by Variable Packet Recording (VPR). In FPR the size of the packets are uniform, while in VPR the size of the packets may vary.
TAO is an incremental recording technique which requires that a track be written in one uninterrupted stream. TAO involves incremental writes that result in multiple tracks, inter-track overhead, and multiple sessions. Since compact discs have a limited number of tracks (typically 99 tracks), TAO is not a suitable method for incremental updates if the user treats the medium as rewritable and performs frequent and numerous updates.
In contrast with TAO, PR can record a track incrementally using packets. A packet includes one or more sectors of a track and is written in an atomic (uninterrupted) write transaction. Typically, a track is filled with packets in a sequential manner. PR can accommodate numerous updates because the number of writes is not limited to the number of tracks. Thus, maintaining a constant stream of data to the recorder is not as critical in PR as it is in TAO.
The ability to recover from error conditions is an additional feature of PR. Each packet is sent in a separate action. If the recorder determines that an error occurred in the transfer or write, the sending of the next packet can be delayed so that the packet can be re-sent.
A CD-R disc may be open (unfixated) or closed (fixated). An open CD-R disc is a CD-R disc with an open session. A closed CD-R disc is a CD-R disc without an open session. Data can be added to an open session, but not to a closed session. However, additional sessions can be added to a closed CD-R disc.
Formats for encoding compact discs include the ISO 9660 standard for encoding CD-ROM discs and the proposed ECMA 168 standard for encoding CD-R discs The specification of the ISO 9660 standard is available from the American National Standards Institute, 1430 Broadway, New York, N.Y. 10018, and is herein incorporated by reference in its entirety. The specification of the ECMA 168 standard is available from the European Computer Manufacturers Association, 114 Rue du Rhone--CH-1204 Geneva, Switzerland and is incorporated herein in its entirety.
Prior systems and methods for incremental recording a CD-R disc do not efficiently use the available storage capacity. In particular, prior systems and methods do not optimize the sizes of the packets to reduce the overhead of implementing a file system compliant with ECMA 168.
In addition, prior systems and methods for incremental recording a CD-R disc do not create a file system which is readable by a conventional CD-ROM drive when the CD-R disc is closed. In particular, prior systems and methods do not result in a closed CD-R disc which is readable by both a CD-R drive compliant with ECMA 168 and a CD-ROM drive compliant with ISO 9660 level 3.
It is desirable to provide a system and method for incremental recording of a CD-R disc which efficiently uses the available storage capacity, and creates a file system which is readable by a conventional CD-ROM drive when the CD-R disc is either open or closed.